Tube Reamer debugging. Need voltages.

[aab0mb]

 I have the tube reamer on perf right now.  The problem I'm having is that the +input of the first half of the opamp reads about HALF of the 1/2 supply voltage (around 2).  All the other pins read in the correct range of 1/2 supply and the 9v+  and ground pins read correctly. 

Pin1=@4.5     Pin8=9v
Pin2=@4.5     Pin7=@4.5
pin3=2.2     Pin6=@4.5
Pin4=0        Pin5=@4.5

I checked the Vref junction and it heads 1/2 supply voltage.  After the 1M where it connects to +input it goes to about half of that.  I've rebuilt the bias network using 22K resistors and the 1M to +in.  It didn't change anything nor did trying a 470k instead of the 1M.  The only things that connect to the +input are the 1M and the input cap. Hmmm.

Does this sound like something that anyone has encountered before?  I'm at a loss here.   Also, if anyone could post correct voltages that would be AWESOME.

-AP-

[aab0mb]

So I'm still at this debugging for the Tube Reamer. 
     It seems that I am unable to get the correct voltage to pin 3 of the opamp.  I assume that I've mis-biased, but I rebuilt the network twice and it still gets pulled down at pin 3.  The circuit passes signal but makes no effect.  The volume pot works to turn the signal down, the gain pot does nothing.  The audio probe did not yield any useful results as it sounds the same all over the circuit.  I'm sure I'll get this thing going after some debugging...  If the problem persists, I'll just start over and see if the next attempt works.


  *ROG Tube Reamer http://runoffgroove.com/tubereamer.html
  *ROG layout 
   Is there a connection between circuit power supply V+ and Gnd. under any of all power supply 'conditions' ie...is there shorting under and 'normal' switching conditions of input jack or DC jack or any other time?
  *YES 
  Measure battery voltage.
  *9VDC
  Measure battery voltage with circuit loading
  *X.21VDC


  Is the circuit npn-negative ground?
  *Transistor type- None
  *Circuit polarity-neg gnd.
  *Opamp type-Dual (TL082)
  connect DMM to ground, and test for continuity at every point in the schematic with a ground symbol, from the most 'distant' [test points should be beyond all connections and solder joints].
  Test the cables that are plugged if they can be plugged in, at the plug sleeves which connect to guitar and amp
  Is there continuity at all 'distant circuit ground points
   *Yes ground continuity check Ok.
  Stage 2
  Connect power supply, if there is a large current draw [ie voltage drops by 10% or more, disconnect power and post that result].
  Is there a >10% voltage drop in battery when circuit is connected?
  * No
  What voltages are measured [using ground as reference voltage =O.0V], using DMM at all active component pins?
  *Dual opamp
*1  4.5v
*2  4.5v
*3  2.2v
*4  0.0v
*5  4.5v
*6  4.5v
*7  4.5v
*8  9v
 
List any pertinent comments and questions.
     I've measured the Voltage divider and in the middle it reads 1/2 supply.  But after the 1M that connects to the +input of the first half of the op amp Voltage reads 2.2  Why is this voltage getting pulled down.  I'm not understanding something I guess. 
 
Stage 3
Audio probe, and list results and comments.
  Test that all stages are 'separated' by DC blocking capacitors,
  Can you physically see that a capacitor is properly wired to the input and output of each active component stage? ie signal path must go through the cap to enter or exit the active stage.
*  In the Tube Reamer there is no blocking cap between stage 1 and stage 2.

still trying,
AP
 

[oskar]

Check that the 2k7 220n net from the first stage is properly grounded.

[frankclarke]

Does it work?

[aab0mb]

Hi guys and thanks for the reply.  No it wasn't working at all besides passing about unity (maybe less) signal.  I just tore it apart and started w/ a new piece of perf.  Right now I have the dip8 socket with power, ground, voltage divider (2x22k), the 22uf cap (I used 10uf), and the 1M going to pin three. Also, the 1M pulldown resistor is attached.

I just checked the voltages with what I have.  The divider is making a good Vref reading.  After the 1M that's connected between the divider and pin 3 it read about half (around 2.20) of Vref.  Same problem as before.  Maybe the parts that I substituted (2x22k and 10uf electro) are pulling the thing out of whack.  If these readings seem correct for the parts that I used, maybe I just had a wiring error or some other problem...

Oskar, yeah I did think that the .22uf/2.7k junction might me a culprit but it didn't yield any positive results when checked over. 

At this point I have just the parts I noted on the board.  I'm wondering if I should just continue building (and checking) with the readings I'm getting or try to figure out my pin 3 problem before moving on.   

Debugging builds character.   

-Aaron-

(edit) I also subbed a 470ohm resistor for the 1K between stages as it's all I had.

[aab0mb]

In this thread http://www.diystompboxes.com/smfforum/index.php?topic=40807.0 the second to the last post seems to mirror my problem.  Is this true?  Could my cheap   $10 DMM be reading the voltage wrong?  If so, I can just continue to build very carefully and it should work. Hopefully...

[Papa_lazerous]

I had a similar problem with a  cheap DMM reading voltages wrong for the same reason as explained in that post.  But the big difference was that my effect was working so I knew the problem was the DMM.......I was just measuring the voltages to compare with other builds.

Seeing how you have started building again, maybe you should be ultra careful with your build and see if it works and not worry too much about the voltages if you are confident what you ahve done so far is correct.  Is your layout proven?  I find if I am working to a layout that I dont know I print out the schem and when I place a component on the perf or vero breadboard and then draw a line through that component and trace on the schem then when I have placed all components the schem should have lines across every connection and component, simple but it works it should help make sure you are not making mistakes that way.  If the effect then works you will know for sure if you have issues with your DMM

[aab0mb]

Thanks Papa Lazerous!  The DMM I have is probably about the lowest quality available.  It was giving me some strange readings on working circuits, so yeah, I bet the DMM is a little bit funny.  At this point I think I will continue to build very carefully and see what the end result is.  I assume that the layout at ROG is correct because there have been a couple of build reports.  I will try the procedure that you recommended about working from the scheme and crossing of components.   Hopefully I can wrap this issue up tonight and move on to the next project.  Fingers crossed.